In many industries involving the distribution of parcels to other locations, the parcels are stacked on top of a skid to form what is called a pallet. Usually, all of the parcels stacked on a particular pallet are to be delivered to one location. These parcels frequently vary in size, shape, and contents. Such parcels usually arrive randomly to the area where they are placed on the pallets. This usually results in a random stacking of such parcels until the pallet is either completely full or may not be stacked higher due to the stacking pattern. The pallets are usually then wrapped by a shrink wrap type plastic material to ensure some integrity of the pallet during the shipping process.
For years, humans have been used to stack parcels onto pallets. Stacking parcels that may weigh up to 65 pounds each for eight hours per shift is a back breaking and monotonous task. As the number of parcels stacked by a human in any one shift increases, the attention to proper stacking and safe palletizing diminishes. In several industries, such inattention results in substantial damage to the contents of the parcels. Furthermore, back injuries and related problems abound for people in such an occupation. In Sweden, for example, the number one injury is back injury due to palletizing.
Industry in general has taken some steps to address the problems of palletizing and injury. In order to stack a more consistent pallet, the "bang wall"technique is frequently applied. In a "bang wall" system, the pallet is placed adjacent to perpendicular walls so that the walls form a corner boundary for the pallet for placing the parcels as the height of the pallet increases. The theory with this system is that by physically confining one corner of the pallet, a reasonable pallet can be constructed every time.
In recent years, it has been recognized that industrial robots may be used to stack parcels onto pallets. However, these applications have typically been limited to palletizing parcels of the same size and weight. In other applications, parcels are stacked in a predetermined pattern as they arrive randomly at the pallet area.
An improved version of a robot stacking system is disclosed in U.S. Pat. No. 4,692,876 to Tenma et al. That patent discloses a system for taking randomly arriving parcels, warehousing them, and then conveying the parcels in a predetermined order to the pickup point to be loaded onto the pallet in predetermined positions. A system such as this requires additional capital investment in a system to automatically warehouse the parcels and then remove them in a particular order and convey them to a robot. It also requires additional time in order to warehouse and redistribute the parcels. While such a system may eliminate problems with human palletizing and injuries therefrom, it is not an economical solution.